Dynamic Steiner Tree Problem

This paper proposes a new problem, which we call the Dynamic Steiner Tree Problem. This is related to multipoint connection routing in communications networks, where the set of nodes to be connected changes over time. This problem can be divided into two cases, one in which rearrangement of existing routes is not allowed and a second in which rearrangement is allowed. In the first case, we show that there is no algorithm whose worst error ratio is less than 1/2 log n where n is the number of nodes to be connected. In the second case, we present an algorithm whose error rate is bounded by a constant and rearrangement is relatively small

Impact of mobility constraints on epidemic broadcast mechanisms in delay-tolerant networks

In this paper, we investigate the effect of mobility constraints on epidemic broadcast mechanisms in DTNs (Delay-Tolerant Networks). Major factors affecting epidemic broadcast performances are its forwarding algorithm and node mobility. The impact of forwarding algorithm and node mobility on epidemic broadcast mechanisms has been actively studied in the literature, but those studies generally use unconstrained mobility models. The objective of this paper is therefore to quantitatively investigate the effect of mobility constraints on epidemic broadcast mechanisms. We evaluate the performances of three classes of epidemic broadcast mechanisms - P-BCAST (PUSH-based BroadCast), SA-BCAST (Self-Adaptive BroadCast), and HP-BCAST (History-based P-BCAST) - with a random waypoint mobility model with mobility constraints. Our finding includes that the existence of mobility constraints significantly improves the reach ability and dissemination speed of epidemic broadcast mechanisms while degrading their efficiency

On scalable modeling of TCP congestion control mechanism for large-scale IP networks

In this paper, we propose an analytic approach of modeling a closed-loop network with multiple feedback loops using fluid-flow approximation. Specifically, we model building blocks of a network (i.e., the congestion control mechanism of TCP, propagation delay of a transmission link, and the buffer of a router) as independent continuous-time systems. By interconnecting these systems, we obtain the model for a complex closed-loop network. We improve the accuracy of analytic models for TCP congestion control and RED router by extending existing fluid-flow models. First, we obtain a block diagram for each continuous-time system using a standard CAD tool widely used in control engineering. Second, we evaluate the performance of a closed-loop network with multiple feedback loops by connecting these block diagrams. We also validate the effectiveness of our analytic approach by comparing our analytic results with simulation results. Unlike other fluid-based modeling approaches, our analytic approach is scalable and accurate; our analytic approach is scalable in terms of the number of TCP connections and routers since both input/output of all continuous-time systems are uniformly defined as a packet transmission rate. Our analytic approach is accurate since the timeout mechanism of TCP and the packet dropping algorithm of RED router are rigorously modeled in our continuous-time systems.

Worst Case Performance of Rayward-Smith\u27s Steiner Tree Heuristic

In this paper, we prove that the worst case performance of the Steiner tree approximation algorithm by Rayward-Smith is within two times optimal and that two is the best bound in the sense that there are instances for which RS will do worse than any value less than two